The words tad yathā mean 'in this way, like this' - indicating that the mantra which has been introduced before tadyathā is what follows tadyathā. My blog post looks at both the Heart Sutra and Medicine Buddha mantras.

The fact that it inadvertently got included in some mantras is down to people not understanding Sanskrit when passing on mantras. Simple as that. But as someone else points out, people are attached to their mantras. We tend to insist on chanting them as received, even if they contain errors. The standard Tibetan explanations of the Vajrasattva mantras have also mangled the Sanskrit original, but no one really wants to hear this. Many Buddhists explicitly or implicitly believe in the infallibility of lineage. But a basic knowledge of Sanskrit will disabuse most people of this affliction when it comes to mantras.

Jayarava wrote:tadyathā is the equivalent a stage direction. I've written about it in some detail on my blog: tadyathā in the Heart Sutra.

The words tad yathā mean 'in this way, like this' - indicating that the mantra which has been introduced before tadyathā is what follows tadyathā. My blog post looks at both the Heart Sutra and Medicine Buddha mantras.

The fact that it inadvertently got included in some mantras is down to people not understanding Sanskrit when passing on mantras. Simple as that. But as someone else points out, people are attached to their mantras. We tend to insist on chanting them as received, even if they contain errors. The standard Tibetan explanations of the Vajrasattva mantras have also mangled the Sanskrit original, but no one really wants to hear this. Many Buddhists explicitly or implicitly believe in the infallibility of lineage. But a basic knowledge of Sanskrit will disabuse most people of this affliction when it comes to mantras.

Different lamas have different opinions about whether we should try to do mantras "correctly" in Sanskrit. If we are, in essence, mentally correcting our guru when we say a mantra differently than he or she does, is that a subtle attitude that we want to carry in to our practice?

Is it just me, or does Tadyatha seems to only precede the mantras of yidams whose practices are at least partially based on Sutras, rather than Tantras (i.e. Shakyamuni Buddha, Medicine Buddha, etc.)?

I've never seen a strictly HYT yidam like Chakrasamvara, Guhyasamaja, or Vajrabhairava have their mantra start with "Tadyatha."

Is this simply a weird coincidence, or is there a pattern at work here?

"The Sutras, Tantras, and Philosophical Scriptures are great in number. However life is short, and intelligence is limited, so it's hard to cover them completely. You may know a lot, but if you don't put it into practice, it's like dying of thirst on the shore of a great lake. Likewise, it happens that a common corpse is found in the bed of a great scholar." ~ Karma Chagme

I may have read into this a bit too much but I would like to offer my opinion.It sounds like tadyatha, literally translated, means "like this, in this way"; relatively translated, the translation can include "spoken like this, the mantra is spoken like this, say the mantra this way, etc" I would like to offer my own thoughts as to the importance of including tadyatha in recitation.Firstly I would say that the literal translation is better to use when contemplating the meaning of the mantra during recitation.

If we take Jayarava's three interpretations, which are interpretations of the translation according to the subject of the mantra, to include correct implications, then the meaning of tadyatha is declarative of the subject at hand - the specific mantra or mind protection.If we consider that reality is like a dream and all manifestations are mind. All sense objects are of mind, etc. We may find that mind protection is influencing the arising of suchness, which is interdependent with the nature of mind, potentiality.

Now it becomes reflexive: as one is reciting the mantra, it is a bit meta to declare that mind is influenced like this, in this way, nonetheless that is the point of including tadyatha in recitation. IOW, to say that what you are doing, mind protection, is arising in this way or like this, followed by the specific protection, is implicitly stating the true meaning of reality and the potential of arising to be less or not at all obscured due to its nature. The nature of arising is an illusion, interdependent with the arising of buddha nature, which is a manifestation of the permanence of potentiality. Potentiality is itself not a permanent thing - therefore buddha nature is primordial but not equiprimordial with potentiality. Since buddha nature includes all aspects of buddhahood as that which is obscured, everything and anything is already those aspects, but is simply appearing according to the net of confusion that makes them appear otherwise. So, tadyatha, in my opinion, means "[it is already] like this..." for instance, "Homage to the Bhagavan Bhaisajyaraguru Vaiduryaprabharaja, a tathagata, an arhat, a samyaksambuddha... [the universe is already existing in a perfect way, according to the power of the potentiality of the buddha, however, to a confused being like me, it appears not to be so, thus I praise you and pray that] in this way (by reciting the following) [reality may manifest according to the following request]: throughout the entire universe, do away with the pain of illness, do away with the pain of spiritual illness, do away with the pain of illness, all throughout. I offer this prayer to you [making it inseparable from reality]." That's my opinion and the way I've come to understand tadyatha, but who knows what the Buddha meant

I do not understand the meaning of Tadyata. So thanks for the kindly explanations. A small contemplation here. Primordial goodness is not seen by persuing things. Then all words have great value as these can help us to reveal nature like it is. In that way it is like nature what we have forgotten and not nature what we need to discover.

According to Khenpo Tsultrim Tenzin, the presence of tadyatha in a mantra indicates that it comes from a sutra tradition rather than a tantra.

Imagine a man who stands before a mirror; a stone strikes it, and it falls to ruin all in an instant. And the man learns that he is himself, and not the mirrored man he had believed himself to be.-- Gene Wolfe